The present invention is in the field of alarm systems. Examples of prior systems of this general type may be appreciated by reference to following U.S. patents: U.S. Pat. No. 4,568,919 to J. Muggli, et al., which issued on Feb. 4, 1986; U.S. Pat. No. 4,752,698 to A. Furuyama, et al., which issued on Jun. 21, 1988; U.S. Pat. No. 4,850,018 to W. R. Vogt, which issued on Jul. 18, 1989; U.S. Pat. No. 4,954,809 to R. W. Right, et al., which issued on Sep. 4, 1990; U.S. Pat. No. 4,962,368 to J. J. Dobrzanski, et al, which issued on Oct. 9, 1990.
The above cited U.S. patents describe systems having control panels that initiate the determination of the states of the units at the various zones or stations in the system by the use of a repetitive polling scheme for polling the detector units or stations from the control panels. In particular, addresses are sent successively on the loop or lines to determine which, if any, units are in an alarm state. Provision is also made in most of these systems to detect trouble conditions in the system.
Many prior art patents describe central control panels having improved intelligence for communication with a plurality of satellite devices. Examples are provided in U.S. Pat. No. 4,901,316 to A. Igarashi, et al., which issued on Feb. 13, 1990; U.S. Pat. No. 5,017,905 to S. Yuchi, which issued on May 12, 1991; and U.S. Pat. No. 5,117,219 to L. D. Tice, et al., which issued on May 26, 1992.
It is also known that the satellite devices themselves may have improved intelligence to perform calculations to determine the likelihood of an alarm related condition. For example, U.S. Pat. No. 5,267,180 to Y. Okayama, which issued on Nov. 30, 1993, entitled FIRE ALARM SYSTEM HAVING PRESTORED FIRE LIKELIHOOD RATIO FUNCTIONS FOR RESPECTIVE FIRE RELATED PHENOMENA provides a system having a plurality of fire detectors connected to a fire receiver for detecting a temperature level, smoke density or gas concentration of a particular surveillance area or zone. Collected information or data inclusive of environmental data of fire related conditions are applied to a respective fire likelihood ratio function and processed by the system in order to improve the accuracy of decision making with respect to fire conditions.
Thus, as provided in the above U.S. patents, complex decisions for alarm systems are determined by one of the components of the system, i.e., either the control panel or the individual satellite devices. Such complex decisions includes calculating a baseline value or analog reference value for each satellite device that characterizes a normal condition for that device. These analog reference values enable the alarm system to compensate for differing environmental conditions within the alarm system's zones of coverage. For example, if a first smoke detector is installed in a normally high temperature zone and a second smoke detector is installed at normally room temperature zone, the reference value of the first smoke detector would be different from the reference value of the second smoke detector in order to compensate for the environmental difference. By continually adjusting the reference value for each smoke detector, optimal system performance is maintained throughout the system.
A significant difference between a present condition of a zone relative to its past condition, indicated by the continually calculated reference value, would indicate a significant change in the environmental conditions, and thus a possible alarm condition, within that zone. The basis of the reference value is variable and dependent upon the detection requirements for the alarm system. For detecting fast developing fires, the reference value may be based on a range of raw data that is collected over a relatively short period of time. In contrast, for detecting slow developing fires, such as a smoldering fire, the reference value must be based on a broader range of raw data that is collected over a much longer period of time. Generally, 24 hours of inertia for collected raw data is required to negate the dilution effections of an extremely slow developing fire.
As stated above, these complex decisions are determined by an existing alarm system in either the control panel or the individual satellite devices that are connected to the control panel. However, both methods have economic and technical drawbacks.
A central control panel or loop controller can determine an alarm condition by continually compiling a running average for each individual sensor. Such control panels have large capacities of memory to store raw data received from the sensors, and thus keep a file history of such data, and powerful Central Processing Units or CPUs to process the raw data. The sensors for such existing systems do not store data in memory or process such data but simply supply the central control panel with the necessary raw data to makes alarm-related decisions.
Central control panels that have large capacities of memory and powerful CPUs require large amounts of continuous loop traffic with each satellite device. Such central control panels must keep track of all raw data collected from each of its satellite devices over a 24 hour period in order to detect extremely slow developing fires. For example, for a control panel that polls each detector every 4 seconds, about 21,600 data samples per device would be necessary in order for the control panel to adequately make alarm reference condition determinations within a given 24 hour period. Accordingly, expensive new communication hardware must be installed, as well as new communication lines that can handle the increased amount of loop traffic; moreover, shielding of the wiring for lower RFI emissions become necessary. In addition, this approach significantly reduces alarm response time since housekeeping chores, such as data quality evaluation and supervision, must be performed by the CPU along with all other tasks.
Similarly, a satellite device can detect a temperature level, smoke density or gas concentration of a particular zone by continually compiling a running average for each individual sensor, such as the device provided in U.S. Pat. No. 5,267,180 to Y. Okayama above. Such device would do all alarm related calculation, including an alarm condition determination, without assistance from the central control panel. Likewise, the control panel would identify an alarm condition only by receiving such an indication from one of its satellite devices. However, in order to make adequate determinations for extremely slow developing fires, as described above, each device requires large capacities of memory and powerful local microprocessors that can be expensive and have large power requirements. Without such capabilities, the precision of alarm condition determinations would be sacrificed for existing alarm systems.
Accordingly, there is a need for an improved alarm system that overcomes the economic and technical drawbacks of existing alarm systems as described above. In particular, there is a need for a alarm system that combines the best advantages of both intelligent control panels and intelligent satellite devices. Therefore, the present invention distributes the various tasks that require substantial intelligence, including the alarm condition detection described above, to the central control panel and satellite devices as well as other devices of the alarm system. This distributed intelligence configuration of the present invention does not require special communication devices and wiring; moreover, it provides optimal performance for certain capabilities, such as detecting extremely slow developing fires.
By relocating or distributing many of the processing tasks from the control panel to the detector, the amount of traffic which must travel between the control panel and each detector is considerably reduced. The advantages of distributing the tasks is that a lower communication rate may be used throughout the entire system. Also, the signal-to-noise ratio, error reduction, and system reliability are improved. Another advantage to a lower communication rate is that special wiring is not required between the control panel and the detectors.
Against the foregoing background, it is a primary object of the present invention to provide an alarm system for detecting and warning of the presence of alarm and trouble conditions in a plurality of zones that distributes various system tasks, such as determining an alarm condition, throughout the system.
It is another object of the present invention to provide a two-tier alarm system in which the various system tasks are handled on a grand scale by a control panel in conjunction with a plurality of intelligent detectors, and on smaller scales by the individual intelligent detectors alone.
It is a further object of the present invention to provide such a two-tier alarm system in which the control panel determines whether an alarm condition exists, particularly for slow developing fires such as smoldering fires.
It is still further object of the present invention to provide such a two-tier alarm system in which the intelligent detector determines whether an alarm condition exists, particularly for fast developing fires.
It is still another object of the present invention to provide a two-tier alarm system for a distributed intelligence system that includes a control panel having processing capabilities that are redundant with functions normally executed by individual detectors. The control panel makes use of such redundant processing capabilities when an operation failure of a detector occurs.